Temperature responsive on-off fluid control device and a control assembly and fire protection system incorporating said device

ABSTRACT

An on-off fluid control device in which a body member has a passage extending therethrough between an inlet adapted for connection to a source of fluid under pressure and an outlet adapted to be connected to a head for discharging the fluid. A gate valve is operable to selectively close the passage and open the passage in response to temperature variations occurring in the vicinity of the body member. The gate valve is initially maintained in its open position despite the existence of a temperature corresponding to the temperature that would normally move it to its closed position, to prevent jamming or locking of the valve. An assembly incorporating the control device in combination with a pressure responsive control device and a fire protection system incorporating the control device.

United States Patent Livingston 51 Jan. 21, 1975 TEMPERATURE RESPONSIVEON-OFF FLUID CONTROL DEVICE AND A CONTROL ASSEMBLY AND FIRE PROTECTIONSYSTEM INCORPORATING SAID DEVICE [75] Inventor: William L. Livingston,Sharon,

Mass.

[73] Assignee: Factory Mutual Research Corporation, Norwood, Mass.

3,802,510 4/1974 Johnson 169/19 Y] YA z-ZIL ,24 28 THERMAL 2 i VALVEPrimary ExaminerM. Henson Wood, Jr. Assistant Examiner-Michael Mar IAttorney, Agent, or FirmLane, Aitken, Dunner 8L Ziems; Warren B. Kice[57] ABSTRACT An on-off fluid control device in which a body member hasa passage extending therethrough between an inlet adapted for connectionto a source of fluid under pressure and an outlet adapted to beconnected to a head for discharging the fluid. A gate valve is operableto selectively close the passage and open the passage in response totemperature variations occurring in the vicinity of the body member. Thegate valve is initially maintained in its open position despite theexistence of a temperature corresponding to the temperature that wouldnormally move it to its closed position,- to prevent jamming or lockingof the valve. An assembly incorporating the control device incombination with a pressure responsive control device and a tireprotection system incorporating the control device.

15 Claims, 4 Drawing Figures PATENIED M21 ms 3.861.473

SHEET 1 OF 2 I %2 2 HERMAL VALVE MOTOR 1 TEMPERATURE RESPONSIVE ON-OFFFLUID CONTROL DEVICE AND A CONTROL ASSEMBLY AND FIRE PROTECTION SYSTEMINCORPORATING SAID DEVICE BACKGROUND OF THE INVENTION 1 Thisinventionrelates to a fluid flow device and a fire protection systemincorporating a plurality of such devices and, more particularly, tosuch a device and sysmeans supported by said body member and movablebetween a first position in which it blocks the flow of fluid throughsaid passage and a second position in which it permits the flow of fluidthrough said passage s and to said head, and control means normallymaintainand permit the discharge of extinguishant therefrom. In

these devices, once the fusible link has melted. or

fused, the head remains open despite later changes in the condition ofthe fire situation in the vicinity of the head. As a result, the openhead remains open despite a later reduction in the intensity of the tirein its immediate vicinity to an extent that the water discharging fromthe head would not be needed at that particular location, which wouldtherefore rob the remaining heads located at a more advantageousposition relative to the tire from valuable extinguishant.

Another type of difficulty that exists in the use of these type systems,as well as in the use of any similar type device employing a movablevalve member for controlling the flow of fluid, is the problem of thevalve member jamming, or locking, in its closed position as a result ofcorrosion, rust, or the like, especially after prolonged periods ofnon-use. Of course, when the valve member jams in its closed positionwhen employed in a fire protection system, the results could bedisastrous.

SUMMARY OF THE INVENTION It is, therefore, an object of the presentinvention to provide a fluid flow control device in which the flow offlow of fluid to and through the head in normal response to a firecondition, yet prevent the flow if the fire situation changes to theextent that the tempera-- ture in the vicinity of the head is reduced.

It is a still furtherobject of the present invention to provide a fireprotection system incorporating a plurality of the above-mentioned fluidcontrol devices.

It is a still further object of the present invention to provide anassembly incorporating the fluid flow control device ofthe presentinvention in combination with a device which also controls the flow ofthe fluid in response to variations in the pressure of the fluid.

Toward the fulfillment ofthese and other objects, the

fluid flow control device discussed above includes a body member havinga passage therethrough and extending between an inlet adapted to beconnected to a source of fluid under pressure and an outlet adapted'tobe connected to a head for discharging said fluid, valve ing said valvemeans in said second position, said control means moving said valvemeans to said first position in response to the temperature in thevicinity of said body member attaining a predetermined, relatively high,value and then falling to a predetermined, relatively low, value.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a vertical cross-sectionalview of the fluid flow control device of the present invention;

FIG. 2 is a horizontal cross-sectional view taken along the line 2-2 ofFIG. I;

FIG. 3 is a reduced, partial elevational view depicting a fireprotection system incorporating a plurality of the fluid control devicesof FIG. I; and

FIG. 4 is a vertical cross-sectional view of an assembly incorporatingthe fluid flow control device of the present invention in combinationwith a pressure responsive control device.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring specifically to FIG. Iof the drawings, the reference numeral 10 refers in general to the flowcontrol device of the present invention which consists of a housing 12having a passage 14 extending therethrough from an inlet opening 14a toan otulet opening 14b. The passage I4 includes an enlarged portion 140which forms a chamber, for reasons to be described in detail later. Thatportion of the housing 12 defining the inlet opening 14a of the passage14 is externally threaded, as shown at I6, while a portion of the innersurface of the passage 14 adjacent the outlet opening 14b has aninternally threaded portion, as shown at 18.

A gate valve member 20 is disposed in the housing I2 and is adapted tomove laterally from an open position shown by the solid lines in FIGS. Iand 2 to a closed position as shown by the dashed lines in which itextends across the passage I4. The valve member 20 is mechanicallyconnected to a thermal valve motor, shown schematically by the referencenumeral 22, which operates to move the valve member to and from its openand closed positions in response to thermal variations in the vicinityof the motor. More specifically, the motor 22 operates to move the valvemember 20 to the left, as

viewed in FIG. 1, towards its closed position in response to apredetermined, relatively low temperature occurring in the immediatevicinity of the motor, and operates to move the valve member tothe-right towards its open position in response to a predetermined,relatively high temperature. Since the thermal valve motor 22 may be ofa conventional type such as the type that operates by the expansion andcontraction of wax or other similar material, it isnot shown ordescribed in any further detail,

An arcuate notch 24 is provided in a portion of the wall of the housingI2 defining the passage l4-in alignment with the valve member 20 forreceiving-the leading end portion of the latter member in its closedposition. I

A restraining sleeve 26 is mounted for slidable movement inside thepassage I4 from an upper position shown by the solid lines to a lowerposition shown by the dashed lines. A notch 28 is formed in theoutersurface of the sleeve 26 which. in the uppcr'position of thesleeve. receives an end portion of the valve member 20 when the valvemember is in its open position. to prevent movement of the valve memberto its closed position.

The upper end of the sleeve 26 is open and a bottom plate 30 extendsacross the lower end thereof. A plurality of openings 31 are formedthrough the bottom plate 30 as well as the lower portion of the wall ofthe sleeve 26, to permit the flow of fluid therethrough for reasons thatwill be explained in detail later. The sleeve 26 is adapted to slidedownwardly in the passage 14 to its lower position shown by the dashedlines in FIG. 1 inv which it releases the valve member 20, underconditions that will be described in detail later.

A slot 32 is provided in the sleeve 26 and a projection 34 is formed onthe inner wall of the housing 12 defining'the passage 14 which extendsin the slot and thus limits the downward movement of'the sleeve 26 inthe passage 14. A leaf spring 40 is mounted on the inner wall of thehousing 12 defining the passage 14 and is adapted to spring outwardlyinto the passage after the sleeve 26 moves to its lower position toretain the sleeve in this position.

The externally threaded portion 16 of the housing 12 is connected to aconduit system or the like via an externally threaded T-connector,,shownpartially by the reference numeral 42, for supplying fluid, suchas'water, to the inlet 14a of the housing. An externally threadedportion of a discharge head, shown partially by the reference numeral44, is threadedly engaged with the threaded portion 18 of the housing 12to dis-' charge the water after it passes through the passage 14;

The head 44 may be of the type which is actuatable by a thermal fuse. orthe like, which opens the head and permits the flow of watertherethrough. The type of head that can be used is disclosed inapplicant's US. Pat. No. 3,743,022 also assigned to the assignee of thepresent invention. The disclosure of the patent is hereby incorporatedby reference.

For the purposes of example, it .will be assumed that the thermal valvemotor 22 is adapted to move the'gate valve member 20 to its closed. flowpreventing position shown by the dashed linesin FIGS. 1- and 2, inresponse to a temperature in the vicinity of the motor of approximatelyl or less, that the head 44 is adapted to open in response to atemperature of approximately l65F., and that the motor 22 is adapted tomove the gate valve to its open, flow. permittingposition,

l, i.e., with the sleeve 26 in its upper position shown by dischargetoward the fire. If the temperature rises to at least 280F., the thermalvalve motor 22 operates to move the valve member 20 from its openposition shown by the solid lines a slight distance. to the right asviewed in FIG. l.The sleeve 26 will then be released and will be forceddownwardly in the passage 14 under the action of the pressuredifferential created by the water flowing through the passage 14 untilit reaches its lower position shown by the dashed lines, in whichfurther downward movement is prevented by the projection 34 engaging theupper portion of the slot 32. In this position, the openings 3] inthewall ofthe sleeve 26 are located in the enlarged portion 141' of thepassage 14 which provides amplespace for the water discharging inalateral direction therethrough as shown by the ber 20 to its closed, orflow preventing position, shown the solid lines in which it preventsmovement of the valve member 20 to the left despite the existence of arelatively low temperature and the resultant urging of the valve memberby the valve motor 22 in this direction.

ofa sufficient magnitude to cause a fusing of the fusible member (notshown) associated with the head 44 and an opening of same. flow will bepermitted through the T-conneetor 42, the passage 14 including the holes31 in the sleeve 26. and out through the outlet 14h as shown by the flowarrows for passage to the head and Assuming a fire occurs in thevicinity of the device 12 by the dashed lines to prevent additional'flowthrough the passage 14. Asa result, water is prevented'from beingindiscriminantly discharged from this particular head in a relativelyinefficient manner, and-is thus saved for use elsewhere.

Of course, in the event the temperaturein the vicinity of the motor 22later rises to or above 280F., the.

motor will move the valve 20 to its open position to permit furtherdischarge through the passage 14 and to V the head 44.

It can be appreciated that the sleeve 26, in initially maintaining thevalve member in its open position, prevents or at least reduces thepossibility of corrosion, rust, or the like, jamming thevalve member 20in a permanently closed position.

FIG. 3 depicts a plurality of control devices 10 of the presentinvention incorporated ina fire protection system shown installed in aspace shown in general by the reference numeral 50. ln particular, apair of branch lines 52 are supported in an elevated position in thespace 50 and extend to either side of a crossmain shown in section bythe reference numeral 54, with a plurality of the T-connectors 42extending" downwardly at spaced intervals along each branch line 52.Each control device 10 is connected to the pendant portion of aT-connector 42 and receivesa discharge head 44, with the connectionsbeing made in the manner described above. i

As stated above, the heads 44 may be in the form of direct dischargenoizles disclosed in the above patent and are disposed directly over aplurality of materials a-f to be protected from fire. Alternatively, theheads {44 can be in the' formfof conventional sprinkler heads in whichthe water is discharged against a serrated disc to create a mist-typespray pattern in a well-knownmanner. r 7

HO. 4 depicts a control assembly incorporating the control device 10 incombinationiwith a device forfalso controlling the flowtoffluid' inresponse to variationsin its pressure. In general, the device 10 isconnected at its discharge end to a discharge head 44 which threadedly,engages the externally threaded portion, 18 of the housing 12 as-in theprevious embodiment.

The pressure responsive control device is shown in from an inlet opening64a to an outlet opening 64b. That portion of the housing 62 definingthe inlet opening 64a of the passage 64 is externally threaded, shown at66 and is connected to a T-connector, shown partially by the referencenumeral 42, of a fluid conduit system, while a portion of the innersurface of the passage 64 adjacent the outlet opening 64b is internallythreaded, as shown at 68 to mate'with the threaded portion 16 of thedevice 10.

A chamber 70 is formed in the housing 62 in communication with thepassage 64 and receives a flow control unit shown in general by thereference numeral 72. The unit 72 is formed by a hollow central portion74 having two hollow stem'portions 76 and 78 extending from oppositesides thereof. The stem portions 76 and 78 extend through openings 80and 82 formed in the housing 62, with the free end portions of each stemportion projecting slightly outwardly from the housing 62.

The central portion 74 of the flow control unit 72 is defined in part bya slightly flexible, disc-like member 84 which is adapted to move froman expanded position shown by the solid lines in FIG. 4 in which it isof a substantially semi-spherical shape, to a retracted po sition shownby the dashed lines in which it takes a substantially concave shape. Inits expanded condition, the movable member 84 seats against a seal ring86 disposed within a cut-out shoulder portion in the interior surface ofthe housing 62, to seal off the flow of fluid through the passage 64. Inthe retracted position of the movable member 84, the seal is broken andfluid can flow from the inlet opening 64a, through the upper portionofthe passage 64 as viewed in FIG. 1,.through the chamber 70 and thelower portion of the passage 64 to the outlet opening 64b. and to theinlet 14a of the control device 10, as shown by the flow arrows. V

The flow control unit 72 contains a pressurized fluid, such as gas,which exerts an upwardly directed force against the movable member 84 tourge it upwardly against the seal ring 86 to prevent the flow of fluidthrough the passage 64. However, this force is selected so as to be lessthan the downwardly directed force against the movable member 84 causedby a predetermined fluid supply pressure which can be attained in theupper portion of the passage 64. As a result, the movable member 84 willmove to its retracted position in response to the pressure ol'the fluidin the upper portion ol'thc chamber 64 attaining or exceeding thispredetermined value, to permit the flow of fluid through the passage 64.

A tip 90 of a fusible material is formed on the end of each stem 76 and78 of the flow control unit 72. The tips 90 normally seal thepressurized gas in the flow control unit 72 and are adapted to melt at apredetermined temperature, such as 5()()F., to permit the release of thepresurrized gas from the unit for reasons that will be described indetail later.

The assembly shown in FIG. 4 is installed in the condition shown in thedrawings, i.e., with the valve member 20 ofthe control unit 10 in itsopen position and the sleeve 26 in its upper position in which itprevents closing ofthe valve member despite relatively low temperatureexisting in the vicinity of the valve'22.

Assuming the T-connector 42 is connected to a conduit system containingwater, and assuming the valve motor 22 and head 44 respond to the sametemperature as discussed in the previous embodiment while the fusibletips are adapted to melt at approximately 500F., I

the operation would be as follows.

lf the pressure of the water in the upper portion of thepassage 64acting on the movable member 84 of the flow control unit 72 is less thana predetermined value. the pressurized gas in the latter unit will forcethe member 64 upwardly into a sealing engagement with the seal ring 86thus preventing the flow of water through the housing 62. Therefore. nowater would be introduced to the control unit 10 or to the head 44despite existence of temperatures sufficient to activate the valve motor22 and open the head 44.

However, if the water pressure in the system is'of a value sufficient toforce the movable member 84 downwardly to the position shown by thedashed lines against the force of the pressurized gas, the water willpass into and through the chamber 70, through the lower portion ofpassage 64 and outwardly through the outlet 64b, where it is introducedinto the inlet 14a of the passage 14 of the control unit 10. Upon a tireoccurring in the vicinity of the assembly of a sufficient magnitude toraise the temperature in the vicinity of the assembly to at least F.,and cause a fusing'of the fusible member (not shown) associated with thehead 44 and an opening of same, flow will be permitted from the controlunit 60 through the passage 14 of the unit 10 including the openings 31in the sleeve 26, and out through the outlet opening 14b to and throughthe head for discharge toward the fire. If the temperature rises to atleast 280F., the thermal valve motor 22 operates to move the valvemember 20 from its open position, shown by the solid lines, a slightdistance to the right as viewed in FIG. 1. The sleeve 26 will then bereleased and will be forced downwardly in the passage 14 under theaction of the pressure differential created by the water flowing throughthe passage, until it reaches the position shown by the dashed lines, inwhich further downward movement is prevented by the projection 34engaging the upper portion of the slot 32. In this position, theopenings 31 of the sleeve 26 are disposed in the enlarged portion 146 of.the passage 14 which provides ample space for the water discharging ina lateral direction therethrough as shown by the flow arrows so not asto substantially impair the flow rate through the passage 14.

In the event the fire later subsides to an extent that the temperaturein the vicinity of the motor 22 drops to approximately lOOF. or .less,the motor will move the valve member 20 to its closed or flow preventingposition shown by the dashed lines to prevent additional flow throughthe assembly.

Ofcourse, in the event the temperature in the vicinity of the motor 22later rises to or above 280F., the motor will move the valve 20 to itsopen position to permit further discharge through the passage 14 and tothe head 44.

During any portion of the above operation of the control device 10,should the water pressure in the system drop below the above-mentionedpredetermined value, the pressurized gas within the flow control unit 72will again force the movable member 84 upwardly against the seal ring 86to prevent any additional flow of fluid through the passage 64 andtherefrom to the control device 10 and the head 44. regardless of thetemperature existing at the time, as long as it is less than 500F.

However, if the temperature in the vicinity of the body member 62 risesto approximately 500?. or greater and thus melts either fusible tip 90,the pressurized gas in the flow control unit 72 will be allowed toescape. the movable member 84 will move downwardly under the force ofthe water, regardless of the latters pressure, and the water will flowthrough the housing 62 to the device 10 where it is subject to theabovementioned further control.

It is thus seen that the assembly of FIG. 4 allows a comprehensivecontrol over the water in response to its pressure and temperatureduring all stages of fire fighting while minimizing the possibility ofstoppage due .to corrosion.

A plurality of assemblies of FIG. 4 can be installed in a fireprotection system in a manner identical to that shown in HQ. 3; Also,one or more assemblies can easily be installed in an eitisting system bysimply inserting it between a conventional discharge head and theconduit system supplying the head.

It is understood that variations may be made in the foregoing withoutdeparting from the scope of the invention. For example, the controldevice of FIG. 1 as well as the control assembly of FIG. 4 can be usedin environments other than fire protection. Also, both the essentialcomponents of the control device 10 and the control device 60 may beincorporated in the same housing or, alternatively, may be incorporatedin the housing, or main body portion, of a discharge head.

Ofcourse, still other variations of the control device, system andassembly disclosed above can be made without departing from the scope ofthe invention as defined inthe appended claims.

I claim:

1. A fluid control device comprising abody member having a passagetherethrough and extending between an inlet adapted to be connected to asource of fluid.

under pressure and an outlet adapted to be connected to a head fordischarging said fluid, valve means supported by said body member andmovable between a first position in which it blocks the flow offluidthrough said passage and a second position in wich it permits the flowof fluid through said passage and to said head, and control meansnormally maintaining said valve means in said second position, saidcontrol means moving said valve means to said first position in responseto the temperature in the vicinity of said body member attaining apredetermined, relatively high, value and then falling to apredetermined, relatively low, value.

2. The device of claim 1 wherein said control means comprises drivemeans responsiveto a said relatively low temperature for urging saidvalve means to said first position, and to a said relatively hightemperature for moving said valve means to said second position, andmeans for maintaining said valve means'in said second position despitethe existence of said relatively low temperature until said relativelyhigh temperature initially occurs.

3. The device of claim 2 wherein said drive means comprises a thermalvalve motor operatively connected to said valve means.

4. The device of claim 2 wherein said maintaining means comprises amember disposed in said passage and adapted to engage said valve meansand prevent movement of said valve means to said first position despitethe existence of said relatively low temperature. said member adapted torelease said engagement in responseto initial movement of said valvemeans toward said second position. V

5. The device of claim 1 wherein said control means is adapted to movesaid valve member back to said second position in response to thetemperature again rising to said relatively high value. 7

6. A fire protection system comprising conduit means disposed in a spaceto be protected from tire and adapted to be connected to a source ofextinguishant, at least one body member connected to said conduit meansand having a passagetherethrough extending between an inlet egisteringwith said' conduit means and on outlet, a discharge head connected tosaid outlet for discharging said fluid, valve means supported by saidbody memberand movable between a first positionin which it blocks theflow ,of fluid through said passage and a second position in which itpermits the flow of fluid through said passage and to said head, andcontrol means normally maintaining said valve means in said secondposition, said control means moving said'valve means to said firstposition in response to the temperaturein the vicinity of said bodymember rising above a predetermined value and then falling to or belowsaid value. i

7. The systemof clairn'6 wherein said control means comprises drivemeans responsive to a said relatively low temperature for urging saidvalve means to said first position, and to a said relatively hightemperature for moving said valve means to said second position, andmeans for maintaining said valve means in said second positiondespite'the existence of said relatively low temperature until saidrelatively high temperature initially occurs. g

8. A fluid control'assembly comprising a housing means having acontinuous passage extending therethrough between an inlet adapted to beconnected to a source of fluid under pressure and anoutlet adapted to beconnected to a head for discharging said fluid. valve means supported bysaid housing and movable between a first portion in which it blocks theflow of fluid through said passage and a second position in which itpermits the flow of fluid through said passage,

control means normally maintaining said: valve means in said secondposition, said control means moving said valve means to said firstposition in response ,to' the temperature in the vicinity of said bodymember attaining a predetermined, relatively high, ivalue and thenfalling to a predetermined,'relatively low, value; a movable membernormally blocking said passage and having one side exposed tofluidpressure in saidpassage, and means including said movable memberfor defining a closed chamber for containing a pressurized fluid, a

said pressurized fluid normally forcing said movable member into saidpassage blocking position, said movable member adapted to move from saidpassage blocking position in response to the fluid pressure in'saidpassage exceeding a predetermined valuefsufficient to overcome the forceof said fluid in said chamber, to permit the flow of fluid insaid'passage.

9. The assembly of claim 8 whereinsaid housing means comprises a pair ofbody members connected together, and having a pair of passagesrespectively m tending therethrough to form said continuous passage. 10.The assembly of claim 8 further comprising means responsive to presenceof a temperature in the vicinity of said body member greater than saidrelatively high temperature. to permit the escape of said fluid fromsaid chamber and permit said movable memher to be forced from saidpassage blocking position by the Fluid in said passage, regardless ofthe pressure of said fluid.

11. The assembly of claim 8 wherein said movable member is adapted tomove back to said passage blocking position in response to the fluidpressure in said pas- .sage dropping below said predetermined value.

13. The assembly of claim 12 wherein said drive means comprises athermal valve motor operatively connected to said valve means.

14. The assembly of claim 12 wherein said maintaining means comprises amember disposed in said passage and adapted to engage said valve meansand prevent movement of said valve means to said first position despitethe existence of said relatively low temperature. said member adapted torelease said engagement in response to initial movement of said valvemeans towards said second position. I 1

15. The assembly of claim 8 wherein said control means is adapted tomove said valve member back to said second position in response to thetemperature again rising to said relatively high value.

1. A fluid control device comprising a body member having a passage therethrough and extending between an inlet adapted to be connected to a source of fluid under pressure and an outlet adapted to be connected to a head for discharging said fluid, valve means supported by said body member and movable between a first position in which it blocks the flow of fluid through said passage and a secoNd position in wich it permits the flow of fluid through said passage and to said head, and control means normally maintaining said valve means in said second position, said control means moving said valve means to said first position in response to the temperature in the vicinity of said body member attaining a predetermined, relatively high, value and then falling to a predetermined, relatively low, value.
 2. The device of claim 1 wherein said control means comprises drive means responsive to a said relatively low temperature for urging said valve means to said first position, and to a said relatively high temperature for moving said valve means to said second position, and means for maintaining said valve means in said second position despite the existence of said relatively low temperature until said relatively high temperature initially occurs.
 3. The device of claim 2 wherein said drive means comprises a thermal valve motor operatively connected to said valve means.
 4. The device of claim 2 wherein said maintaining means comprises a member disposed in said passage and adapted to engage said valve means and prevent movement of said valve means to said first position despite the existence of said relatively low temperature, said member adapted to release said engagement in response to initial movement of said valve means toward said second position.
 5. The device of claim 1 wherein said control means is adapted to move said valve member back to said second position in response to the temperature again rising to said relatively high value.
 6. A fire protection system comprising conduit means disposed in a space to be protected from fire and adapted to be connected to a source of extinguishant, at least one body member connected to said conduit means and having a passage therethrough extending between an inlet registering with said conduit means and on outlet, a discharge head connected to said outlet for discharging said fluid, valve means supported by said body member and movable between a first position in which it blocks the flow of fluid through said passage and a second position in which it permits the flow of fluid through said passage and to said head, and control means normally maintaining said valve means in said second position, said control means moving said valve means to said first position in response to the temperature in the vicinity of said body member rising above a predetermined value and then falling to or below said value.
 7. The system of claim 6 wherein said control means comprises drive means responsive to a said relatively low temperature for urging said valve means to said first position, and to a said relatively high temperature for moving said valve means to said second position, and means for maintaining said valve means in said second position despite the existence of said relatively low temperature until said relatively high temperature initially occurs.
 8. A fluid control assembly comprising a housing means having a continuous passage extending therethrough between an inlet adapted to be connected to a source of fluid under pressure and an outlet adapted to be connected to a head for discharging said fluid, valve means supported by said housing and movable between a first portion in which it blocks the flow of fluid through said passage and a second position in which it permits the flow of fluid through said passage, control means normally maintaining said valve means in said second position, said control means moving said valve means to said first position in response to the temperature in the vicinity of said body member attaining a predetermined, relatively high, value and then falling to a predetermined, relatively low, value; a movable member normally blocking said passage and having one side exposed to fluid pressure in said passage, and means including said movable member for defining a closed chamber for containing a pressurized fluid, said pressurized fluid normally forcing said movable member into said passage blockiNg position, said movable member adapted to move from said passage blocking position in response to the fluid pressure in said passage exceeding a predetermined value sufficient to overcome the force of said fluid in said chamber, to permit the flow of fluid in said passage.
 9. The assembly of claim 8 wherein said housing means comprises a pair of body members connected together, and having a pair of passages respectively extending therethrough to form said continuous passage.
 10. The assembly of claim 8 further comprising means responsive to presence of a temperature in the vicinity of said body member greater than said relatively high temperature, to permit the escape of said fluid from said chamber and permit said movable member to be forced from said passage blocking position by the fluid in said passage, regardless of the pressure of said fluid.
 11. The assembly of claim 8 wherein said movable member is adapted to move back to said passage blocking position in response to the fluid pressure in said passage dropping below said predetermined value.
 12. The assembly of claim 8 wherein said control means comprises drive means responsive to a said relatively low temperature for urging said valve means to said first position, and to a said relatively high temperature for moving said valve means to said second position, and means for maintaining said valve means in said second position despite the existence of said relatively low temperature until said relatively high temperature initially occurs.
 13. The assembly of claim 12 wherein said drive means comprises a thermal valve motor operatively connected to said valve means.
 14. The assembly of claim 12 wherein said maintaining means comprises a member disposed in said passage and adapted to engage said valve means and prevent movement of said valve means to said first position despite the existence of said relatively low temperature, said member adapted to release said engagement in response to initial movement of said valve means towards said second position.
 15. The assembly of claim 8 wherein said control means is adapted to move said valve member back to said second position in response to the temperature again rising to said relatively high value. 